> How about the 6845 CGA (?) VDU Controller, should be loads of them about and
> still fairly easy to use?

Here's why not to use the 6845, according to Steve Jobs in the article
"An Interview: The Macintosh Design Team" in the February 1984 issue of Byte
magazine:

Steve Jobs:  Do you realize that in an IBM PC the video board, just the
    black-and-white video plug-in card, has got way more chips than the entire
    Macintosh?"
[...]
Steve Jobs:  I just thought I'd show this to you.  This is the IBM video
    board; it's only video, nothing else.  It's 69 integrated circuits, more
    chips than an entire Macintosh, and it basically does nothing.  And it
    doesn't even do that very well.
Chris Espinosa:  Fourty percent more chips than the Mac.
Steve Jobs:  So that sort of gives you a feeling.  And again, this just has
    the video on it.  Macintosh, in addition to having video that's far
    higher in resolution and far faster, [...]
[...]
Steve Jobs:  If you bite into that IBM display board, it'll totally flicker
    if you do it at the wrong time.

He was referring to the IBM Monochrome Display Adapter (MDA).  And although
he mentions the low resolution and fliker, he left out an even more scathing
criticism of the MDA card:  It couldn't do bit-mapped graphics at all!  For
years video cards for PC clones have used high-integration ASICs (which usually
contain a functional equivalent of a 6845).

The 6845 was useful in the late 70s and early 80s, and could replace a fair
number of TTL MSI chips, but it isn't a very good choice for new designs today
because you still have to add a bunch of additional chips to make it do
anything useful, and because it is an NMOS chip and draws quite a bit of power
by today's standards.

The 6845 might be useful if you want to build a one-of-a-kind device (and thus
can't engineer something more modern), but the original poster was hoping to
find something highly integrated, small, cheap, and with a simple bit-serial
interface.

The TI TMS9118 and TMS9918 families provided a much higher integration
solution, and saw widespread use in the TI 99/4 home computer and the
Japanese MSX computers.  All you have to add is a pair of 16K*4 DRAMs.  They
have a simple 8-bit parallel interface.  Unfortunately the availability is
poor now, and they were also NMOS.  Yamaha LSI makes the V9938 and V9958,
which are software compatible upgrades from the TI parts, but I'm not sure
how available they are.

It would seem that the ideal single-chip solution could now be built in a DRAM
process and contain a frame buffer, a simple processor, and a small masked ROM
with code and character sets.  I wonder whether any DRAM vendors have
considered making such a thing.  It's sort of a logical evolution from VRAM,
although it probably wouldn't be useful in PCs or workstatons.

Of course, you could just build a gate array and use a standard DRAM or VRAM
and a DAC to build a three-chip solution.  The gate array could even provide
digitally generated NTSC or PAL color encoding.

Cheers,
Eric